RGB means R, G, B channel if Linear RAW or Data processed as Post;
1. RAW RGB; Original Linear RAW from Sensor, so waveform of RAW RGB or luma shows relatively low; 20~30% is OK for most cases; If RAW RGB/luma exceeds 100%, it must be overexposed.
2. Post RGB; Linear RAW from sensor, logged then load LUT to resemble final grading output. So waveform of Post RGB/luma shows normal image which is supposed to be close to final output. For most cases, 70~80% of waveform is OK. Note: if waveform exceeds 100%, that does not mean overexposed.